1. Field of the Invention
The present invention relates to a semiconductor laser device having a function of detecting reproduction signals and various servosignals. The device is incorporated into an optical head, which is a main component of an optical information processing device that records, reproduces, and erases information on an optical recording medium.
2. Description of the Related Art
Generally, for accurately reading signals recorded on an optical recording medium such as an optical disk, focus/tracking errors caused by surface oscillation or off center rotation of a rotating disk need to be detected as signals and adjusted by a focus/tracking servo actuator.
For detection of the focus/tracking error signals and reproduction signals, a semiconductor laser device illustrated in FIG. 20 has been used conventionally. The structure and the operational principle of this device will be explained in the following. Broken lines in FIG. 20 show either an outgoing light beam from a semiconductor laser element 101 or a reflected light beam from an optical recording medium 105. The elements in cross section are only partially provided with hatching for clarity.
A light beam emitted from a light source, i.e. the semiconductor laser element 101, is diffracted by a 3-beam formation diffraction grating element 102 in the direction Y indicated in the drawing, and the zero-order diffracted light is branched into a main beam and the first xc2x1 order diffracted light is branched into sub-beams. The light paths of these three branched light rays are deflected at an angle of 90xc2x0 by a beam splitter 103 and focused by focusing means, e g. an objective lens 104, onto the optical recording medium 105. The light beam reflected by the optical recording medium 105 enters a light beam branching element, i.e. a hologram optical element 106. The hologram optical element 106 is provided with diffraction gratings that have a lens effect. The light beam reflected by the optical recording medium 105 is led by the hologram optical element 106 to photodetector element groups 109 and 110. Among the reflected light beams led to the photodetector element groups 109 and 110, reproduction signals and focus error signals are detected from the main beam, and tracking error signals are detected from the sub-beams. Moreover, the objective lens 104 is provided in an actuator and driven on the basis of the detected focus/tracking error signals in the optical-axial direction and in the direction perpendicular to the track.
However, the conventional semiconductor laser device illustrated in FIG. 20 has many optical components that also need to be arranged individually, so that the device cannot be miniaturized easily. Furthermore, since each optical component is positioned discretely, it is necessary to take a lot of trouble for adjusting and fixing each position. In particular, since the relative position between the hologram optical element 106 and the photodetector element groups 109, 110 has a great influence on the characteristics of reproduction signals and focus/tracking error signals, position adjustment with high-precision has been required. Therefore, a great deal of time and cost are necessary for assembling. In addition, slight misregistration during and after assembly causes deterioration of the characteristics.
It is an object of the present invention to solve the conventional problems described above by providing a miniature semiconductor laser device that can be assembled without complicated position adjustment.
A semiconductor laser device of the present invention includes a semiconductor laser element, a light beam branching element for branching a light beam emitted from the semiconductor laser element and reflected by an optical recording medium into a plurality of light beams, a light beam reflector for reflecting the light beam branched by the light beam branching element, and a detector portion for detecting the light beam reflected by the light beam reflector. The light beam branching element and the detector portion are formed on the same substrate.
According to the configuration described above, the light beam branching element and a plurality of detector portions are integrated on the same substrate, so that the miniaturization of the device is achieved. Furthermore, since the relative position between the light beam branching element and the plurality of detector portions is determined at the time when the substrate is formed, position adjustment with high-precision is no longer necessary during assembly, and moreover, the deterioration of characteristics arising from slight misregistration during and after assembly can be avoided.